blame: -C -C -C

blame: -C -C -C

When you do this, existing "blame -C -C" would not find that the
latter half of the file2 came from the existing file1:

	... both file1 and file2 are tracked ...
	$ cat file1 >>file2
	$ git add file1 file2
	$ git commit

This is because we avoid the expensive find-copies-harder code
that makes unchanged file (in this case, file1) as a candidate
for copy & paste source when annotating an existing file
(file2).  The third -C now allows it.  However, this obviously
makes the process very expensive.  We've actually seen this
patch before, but I dismissed it because it covers such a narrow
(and arguably stupid) corner case.

Signed-off-by: Junio C Hamano <junkio@cox.net>